Sliding clamps are topologically-closed rings that can encircle the DNA double h
ID: 54872 • Letter: S
Question
Sliding clamps are topologically-closed rings that can encircle the DNA double helix. How, then, are they able to get on and off of the DNA? What is the purpose of this striking topology? Sliding clamps are topologically-closed rings that can encircle the DNA double helix. How, then, are they able to get on and off of the DNA? What is the purpose of this striking topology? Sliding clamps are topologically-closed rings that can encircle the DNA double helix. How, then, are they able to get on and off of the DNA? What is the purpose of this striking topology?Explanation / Answer
In the case of bacteria, the beta subunit plays the role of the sliding clamps while in the case of eukaryotes, the PCNA plays the role of the sliding clamps.
The beta subunit is active as a homo dimer, each monomer contributing 40.5kDa (total molecular weight =81kDa).
While the PCNA is active as a homotrimer, each monomer contributing 27kDa (total molecular weight = 87kDa) which are quite similar. They both have a six-fold symmetry.
The domains even though they donot have much sequnce similarity, they are superimposable.
Each domain contains two a-helices that line the central cavity and are perpendicular to the DNA. The a-helices are supported by a continuous layer of b-sheet structures all around the outside that forms the intermolecular boundaries.
The sliding clamps are proteins and would be repelled by DNA. However, the charge distribution on the ring is asymmetric. The outer surface has strong negative electrostatic potential, which may prevent the clamp from nonspecific interactions with DNA. The inside of the central cavity, where the DNA is located, has a net positive electrostatic potential and, thus, may strengthen the interaction with DNA upon proper assembly of the ring around by the clamp loader.
The purpose of this topology is that the DNA polymerase sliding clamp encircles DNA and gives the polymerase its high processivity by tethering the polymerase to the DNA.
Related Questions
drjack9650@gmail.com
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.